The present application relates to plasma arc torches, particularly plasma arc torches of the so-called blow-back type.
Plasma torches are commonly used for cutting or marking metal work pieces. In general, plasma torches use an electrode to generate an electric arc within the torch. A high velocity gas is flowed through the torch, and the electric arc ionizes the gas, creating a plasma. The high velocity stream of ionized gas, or plasma, is delivered through a nozzle of the torch towards the work piece that is to be cut. The plasma serves to conduct electricity from the torch to the work piece. In this way, the plasma heats the work piece, melting the metal in the location of the cut, and mechanically blows the molten metal away to form the cut.
In blow-back torches, the nozzle is generally fixed with respect to the torch body, and the electrode is displaceable with respect to the nozzle. Initially, the electrode is in contact with the nozzle. When the blow-back torch is activated, for example through a user's actuation of a trigger, a voltage differential is applied between the nozzle and the electrode, and a plasma gas (such as air) flows through the torch to the nozzle. The gas flow causes the electrode to “blow back” out of contact with the nozzle, establishing a pilot arc between the electrode and the nozzle. At the same time, the gas flows out of the nozzle, transferring the arc to the work piece to perform the torch operation.
In blow-forward torches, the electrode is generally fixed with respect to the torch body, and the nozzle is displaceable with respect to the electrode. As with blow-back torches, the nozzle is initially in contact with the electrode. Once the blow-forward torch is activated, however, and the voltage differential is applied between the nozzle and the electrode, the flow of plasma gas causes the nozzle to “blow forward” out of contact with the nozzle. In this way, the pilot arc is established between the electrode and the nozzle, and gas flows out of the nozzle, transferring the arc to the work piece as described above.
Users of plasma torches (blow-back and blow-forward) are often required to replace the electrode used in the torch as the electrode experiences wear during plasma torch operations. The use of an excessively worn electrode may cause damage to the plasma torch and the work piece and, more importantly, may present safety concerns to the user of the plasma torch.
Applicant has thus discovered that it would be desirable to provide a plasma torch in which the electrode wear can be detected and the use of an excessively worn electrode can be prevented. As described in greater detail below, a variety of challenges were identified and overcome through Applicant's efforts to invent and develop such a plasma torch.